Heretofore, a magnetic shielding apparatus which was used for measuring biomagnetism generated from an organism and which screened an environmental magnetic field (an external magnetic field) was manufactured by fastening and fixing a plate having high permeability (high-permeability material such as Permalloy) onto a frame made of aluminum and stainless steel without clearance by a bolt and others as a spatially closed box-type chamber. Besides, plates made of Permalloy were laminated, a magnetic shielding factor was enhanced, and a plate made of high-electric conductivity material such as aluminum was used for screening an electromagnetic wave. A small-sized light cylindrical magnetic shielding apparatus using sheet material having high permeability in place of Permalloy is reported (for example, see patent document 1).
It is known that the magnetic shielding factor of the cylindrical magnetic shielding apparatus is higher in a direction perpendicular to a cylindrical axis than in a direction of the cylindrical axis. Therefore, in case a magnetic field is measured inside the cylindrical magnetic shielding apparatus, a magnetic field component in the direction perpendicular to the cylindrical axis is often measured. In the measurement of biomagnetism in which a minute magnetic field is detected, a SQUID fluxmeter using a superconducting quantum interference device (SQUID) is generally used. For a method of inserting an object of examination inside the cylindrical magnetic shielding apparatus, two methods of (1) a method of inserting an object of examination from either open end at both ends of the cylindrical magnetic shielding apparatus and (2) a method of providing an openable door to the cylindrical magnetic shielding apparatus and inserting an object of examination via it are proposed (for example, see patent document 1.
[patent document 1] JP-A No. 136492/2002